(1) Field of the Invention
The present invention relates to a transfer device and an image forming apparatus using the same, and in particular relates to a transfer device which is used in an image forming apparatus such as an electrostatic copier, laser printer, facsimile machine or the like that forms images with toner based on electrophotography and which transfers the toner image formed on the peripheral side of an image bearer by means of an endless belt as well as to an image forming apparatus using the same device.
(2) Description of the Prior Art
Conventionally, image forming apparatuses based on electrophotography such as copiers, printers, facsimile machines and the like have been known. In these image forming apparatuses based on electrophotographic technique, image forming is performed by forming an electrostatic latent image on the photoreceptor drum (toner image bearer) surface, supplying toner to the photoreceptor drum from a developing device to develop the electrostatic latent image, transferring the toner image that has been formed on the photoreceptor drum by development to a sheet such as paper or the like, and fixing the toner image onto the sheet by means of a fixing device.
In image forming of the image forming apparatus, there are two kinds of transfer methods: one method is that the toner image is directly transferred from the photoreceptor drum to the recording medium and the other method is known as a so-called intermediate transfer method in which the toner image is transferred from the photoreceptor drum to the intermediate transfer medium and then the toner image is transferred to the recording medium. In the image forming apparatus using the intermediate transfer mechanism, an endless intermediate transfer belt is often used as the intermediate transfer medium.
In the image forming apparatus using the intermediate transfer belt, the toner image formed on the peripheral side of the photoreceptor drum is temporarily transferred to the intermediate transfer belt. Particularly, in an image forming apparatus that supports both monochrome and color printing, a plurality of photoreceptor drums for individual colors are arranged along the intermediate transfer belt so that the toner images of different colors are sequentially transferred to the intermediate transfer belt, one over the other. Then the toner image thus formed on the intermediate transfer belt is transferred to the paper.
The intermediate transfer belt used for the above image forming apparatus is generally formed by injection molding and then spreading the molding so as to have a predetermined thinness and length by blow molding or die-molding.
However, the thus formed intermediate transfer belt will present variation in expansion coefficient from one point to another because of uneven distribution of the resin material and the conductive components mixed in the resin material. As a result, the circumference of the belt slightly varies across the belt width.
Accordingly, the intermediate transfer belt suffers the problem of the belt skewing during circulatively traveling due to the difference in circumference depending on the points across the belt width and due to variation in dimensional accuracy and attachment accuracy of the roller members (drive roller, driven roller, etc.) that support and stretch the intermediate transfer belt.
To deal with this, in order to prevent the intermediate transfer belt from skewing, there is a known technology of preventing intermediate transfer belt 61 from skewing by providing a pair of projections (which will be referred to hereinbelow as “beads”) 6610 along both the edges, with respect to the width direction of the belt, on the interior peripheral surface of intermediate transfer belt 61 as guide elements for guiding the conveyance of intermediate transfer belt 61 as shown in FIGS. 1A and 1B. These beads are brought in sliding contact with both the end faces of each roller member that supports and stretches intermediate transfer belt 61 to guide intermediate transfer belt 61 being conveyed, whereby skewing of the belt can be prevented.
When bead 6610 is provided for endless intermediate transfer belt 61, each strip-like bead 6610 is formed annularly so that both ends, designated at 6611 and 6612 of bead 6610 are arranged so as to oppose each other with a predetermined distance apart therebetween. This gap serves as a positioning mark. The positioning portion of conventional bead 6610 is usually defined by simple surface (which will be referred to hereinbelow as “perpendicular surface”) 6611a and 6612a that are perpendicular to the advancing direction (moving direction) of the intermediate transfer belt.
However, if the positioning mark of bead 6610 is formed by perpendicular surface 6611a and 6612a alone, there occurs the problem that the roller members are prone to run up on bead 6610. This occurs because the gap in the positioning mark of bead 6610 and each of the roller members are arranged parallel, so that the roller member easily enters the gap in the positioning mark.
There is also another problem that if the positioning mark of bead 6610 collides with the endface of the roller member, the edges of the positioning mark are prone to deform and peel off.
In order to solve the above problem, there has been a disclosed technology shown in FIGS. 2A and 2B in which the positioning mark defined by both ends 7611a and 7612a (7611b and 7612b) of each of bead 7610a (7610b) for guiding conveyance of intermediate transfer belt 61 is formed by an inclined surface 7611a1 and 7612a1 (7611b1 and 7612b1) that are inclined relative to the advancing direction of intermediate transfer belt 61 (see patent document 1: Japanese Patent Application Laid-open H04-242280).
This configuration of patent document 1, however, has the problem that when the positioning mark at each of beads 7610a and 7610b is formed of only inclined surface 7611a1 and 7612a (7611b1 and 7612b1) that are inclined relative to the advancing direction of intermediate transfer belt 61, it is impossible to keep the bonding strength high enough at the tip of the inclination, hence beads 7610a and 7610b are highly likely to peel off from intermediate transfer belt 61.